They are generally believed to be tiny 'eyes', too small to be seen unaided, embedded in the organism's shell,[1] acting in unison to function as a large, dispersed, compound eye.
[2] However, in 2013 studies suggested that aesthetes may serve the function of releasing material to repair the periostracum, a proteinaceous material covering the shell and protecting it from abrasion.
[3] This turned out to be false, as it was conclusively demonstrated in November 2015, that aesthetes are image forming eyes.
[4] This layer is constantly worn away by waves and debris as a function of their rugged habitat, and must be continuously replaced to protect the shell.
Some chitons also have larger lens-bearing eyes.